It is known that providing an electric current proximate an underwater surface in a saltwater environment inhibits and deters the growth of marine organisms, such as barnacles. It is believed that certain marine organisms, such as barnacles, abhor chlorine. When electric current is provided in a saltwater environment, the current interacts with the surrounding saltwater and produces chlorine gas, among other things, in the form of chemically adsorbed species and bubbles at the underwater surface. The production of chlorine increases with the current flow.
The following U.S. Patents, each of which are incorporated herein by reference in entirety, disclose propulsion arrangements for marine vessels and anti-fouling systems and methods for marine structures, including for example cathodic protection systems.
U.S. Pat. No. 3,953,742 discloses a cathodic protection system monitor that is coupled to an impressed current cathodic protection circuit and used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode (LED) lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
U.S. Pat. No. 4,492,877 discloses an electrode apparatus for mounting an anode and reference electrode of a cathodic protection system on an outboard drive unit. The apparatus includes an insulating housing on which the anode and reference electrode are mounted and a copper shield mounted between the anode and electrode to allow them to be mounted in close proximity to each other. The shield is electrically connected to the device to be protected and serves to match the electrical field potential at the reference electrode to that of a point on the outboard drive unit remote from the housing.
U.S. Pat. No. 4,528,460 discloses a control system for cathodically protecting an outboard drive unit from corrosion, which includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.
U.S. Pat. No. 6,183,625 discloses a galvanic monitor system that uses two annunciators, such as light emitting diodes, to alert a boat operator of the current status of the boat's galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciators lights are used to inform the operator if the protection is proper or if the component to be protected is either being over protected or under protected.
U.S. Pat. No. 6,209,472 discloses a system for inhibiting marine organism growth on underwater surfaces. The system provides an electric current generator which causes an electric current to flow proximate the underwater surface. A source of power, such as a battery, provides electrical power to the electric current generator. The flow of current passes from the underwater surface through water surrounding the surface or in contact with the surface, and a point of ground potential. The point of ground potential can be a marine propulsion system attached to a boat on which the underwater surface is contained.
U.S. Pat. No. 7,131,877 discloses a marine cathodic protection system that maintains a submerged portion of a marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a preselected constant potential in response to the sensed potential at a closely located reference electrode during normal operations. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.
U.S. Pat. No. 7,305,928 discloses a vessel positioning system that maneuvers a marine vessel in such a way that the vessel maintains its global position and heading in accordance with a desired position and heading selected by the operator of the marine vessel. When used in conjunction with a joystick, the operator of the marine vessel can place the system in a station keeping enabled mode and the system then maintains the desired position obtained upon the initial change in the joystick from an active mode to an inactive mode. In this way, the operator can selectively maneuver the marine vessel manually and, when the joystick is released, the vessel will maintain the position in which it was at the instant the operator stopped maneuvering it with the joystick.
U.S. Pat. No. 7,381,312 discloses a ceramic conductor, which is supported by an electrically insulative support member for attachment directly to a marine propulsion drive and for use as either an anode or electrode in a corrosion prevention system. The ceramic conductor is received within a depression formed in a surface of the electrically insulative support member and the exposed surface of the ceramic conductor can be offset from or coplanar with an exposed surface of the electrically insulative support member. The ceramic conductor can comprise oxides of iridium, tantalum and titanium that are formed as a coating on a titanium substrate.
U.S. Pat. No. 8,118,983 discloses a corrosion inhibiting system, which is provided with the ability to allow both primary and secondary portions of the circuit to be used in the alternative without having the primary and secondary systems interfere with each other by operating at the same time. By incorporating a continuity controller, such as a switch or a diode to selectively disconnect the sacrificial anode from the circuit, the primary and secondary systems can both be provided on a marine vessel, but used independently from each other. In that way, the primary and secondary corrosion inhibiting systems are prevented from interfering with each other during normal operation.
U.S. Pat. Nos. 4,322,633; 6,173,669; 6,547,952; 6,822,462; 6,973,890; 7,025,013; 7,064,459; 7,211,173; 7,686,936; 8,372,260 are also relevant background and are incorporated herein by reference.